This invention relates to an improved system for pumping crude oil from an earth formation, and in particular to such a system that reduces or eliminates the undesirable admission of gas into the pump column.
With conventional crude oil recovery systems, a downhole pump is positioned inside a borehole in an earth formation, and crude oil is drawn by suction through perforations just below the pump inlet. Crude oil and any salt water or gas passing through the perforations are drawn into the downhole pump and via the pump into the pump column. Natural gas that rises up the pump column is then routed to the battery tanks, where it is either vented to atmosphere or burned. If sufficient natural gas is being produced, it can be captured for distribution or for use in powering the engine driving the pump.
As the gas rises in the pump column, it expands and can build up sufficient pressure to force the column of oil above the expanding gas out of the well head. Once the expanding column of gas displaces oil in the pump column, the reciprocating polish rod that powers the downhole pump is deprived of contact with heat-dissipating oil. As a result, the polish rod can become very hot, and the rate of wear of the polish rod can substantially increase.
Thus, a need presently exists for an improved crude oil recovery system that reduces or eliminates the pumping of natural gas into the pump column.
By way of general introduction, the crude oil recovery system illustrated in the drawings includes a downhole pump having a pump inlet and a pump outlet. An extension is provided that extends substantially below the pump inlet, and this extension is provided with an extension inlet. All of the fluid pumped by the pump passes through the extension inlet, and this extension inlet is positioned below the lowest level of crude oil in the borehole that is created by the pump. For this reason, the extension inlet remains submerged in the crude oil pooled in the borehole, and gas is prevented from entering the pump or the pump column. Instead, the gas pressurizes the borehole annulus, where it can readily be collected or vented.